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A spectrum efficient modulation technique known as Amplitude Companded Sideband (ACSB) has recently been developed for land mobile radio. This technique uses single sideband modulation with baseband processing in the form of amplitude companding and spectral shaping, along with a pilot signal which provides AGC, AFC, squelch and selective call functions. The resulting system performs as well as or better than commercial FM systems and uses only one-fifth the bandwidth. In this paper, an efficient algorithm which incorporates the various factors affecting the performance of a mobile radio system is developed, and used to compare the efficiency and service quality of both FM and ACSB radios. The ACSB radios have 1.5 to 2 times the range of an FM radio with equal power. With regards to adjacent channel interference, ACSB with 5 kHz channel separation performs as well as FM with 20 or 25 kHz separation. When both co-channel and adjacent channel interference are taken into account, ACSB is about 6 to 8 times more efficient than FM in terms of maximizing the number of users supported per MHz in a given service area.